Due to increasing concern about the side effects of oral contraceptives and IUD's, there is renewed interest in barrier contraceptives by health care providers, government regulatory officials and consumers. Barrier methods of contraception have been in scientific eclipse for almost two decades but there has been a recent shift of interest back to these traditional methods of fertility regulation.
The prior art is replete with intravaginal materials useful as contraceptives and medicaments. The goal in these contraceptive methods has been to provide an effective, efficient and convenient means of preventing sperm from reaching the cervical uterine canal. The normal vagina maintains an acid pH of from 4 to 5 and in this environment spermatozoa have motility and viability for a relatively short period of time, i.e. about 1 to 2 hours. On the other hand, sperm maintain their motility and viability in the uterine cervix for up to 48 hours. The objective of all barrier contraception is to prevent sperm from entering the uterine cervix and subsequently fertilizing an ovum in the fallopian tube.
The diaphragm was introduced by an English pharmacist, Mensinga, in the 1880's. Used alone or in conjunction with spermicidal cream, foam, suppository preparation or jelly, it can be an effective contraceptive device when used correctly and consistently. Creams, foams, suppositories and jellies alone statistically provide less protection against unwanted pregnancies. All of the aforementioned contraceptive methods have inherent deficiencies: they tend to interfere with the coital act due to their relatively short duration of effectiveness, and a high level of motivation is required for their correct and consistent usage. Thus, any invention that provides a more convenient or longer acting vaginal contraceptive method would represent a significant improvement in the state of the art.
The active agent found in many of the current spermicidal preparations is a nonionic surfactant such as nonylphenoxypoly(ethyleneoxy)ethanol, also known as nonoxynol-9, or p-diisobutylphenoxypolyethoxyethanol. Other agents known to be effective include bactericides such as benzethonium chloride, chemically known as N,N-dimethyl-N-[2-[2-[4-(1,1,3,3-tetramethylbutyl)-phenoxy]ethoxy]ethyl]be nzenemethanaminium chloride, phenyl mercuric acetate, and acids such as boric acid and tartaric acid.
Several approaches to providing vaginal contraceptive methods with improved duration of effectiveness have been reported in the literature. For example, U.S. Pat. Nos. 3,991,760, 3,995,633, 3,995,634, 4,031,202 and 4,073,833 disclose intravaginal devices that continuously release nonionic surfactant to create a spermicidal environment within the vagina. A serious disadvantage of these approaches is that the surfactant is delivered to the vagina constantly whether needed or not. Thus, the woman is exposed to a much higher level of surfactant than with devices such as the diaphragm and cream or jelly intended for intermittent-use. Since creams or jellies occasionally produce irritation such as a burning sensation, the continuous-release approach is certain to worsen this problem. Moreover, it has recently been reported that nonoxynol-9 is capable of being absorbed into the bloodstream through the vaginal mucosa. This fact suggests that continuous administration of spermicidal surfactants may not provide the same degree of toxicological safety as intermittent administration.
Barrier contraceptive sponges are known in the prior art. U.S. Pat. No. 3,762,414 describes an improved configuration of a rubber sponge for contraceptive use and Republic of South Africa Pat. No. 767,523 describes a sponge made from collagen.
Vaginal contraceptives that rely on an acid pH are also well known in the prior art. Indeed, the historical contraceptive use of rose hips and lemons which are characteristically of low pH is known. U.S. Pat. No. 4,027,670 discloses a contraceptive device containing a contraceptive gel. The gel includes citric acid and has a pH of approximately 2. U.S. Pat. No. 2,149,240 and U.S. Pat. No. 2,330,846 disclose acid vaginal preparations useful as contraceptives. However, such preparations are not residual.
Fibrous materials are well known for their use as tampons and are disclosed in U.S. Pat. Nos. 2,202,566, 3,067,743, 3,067,745 and 4,186,742. The latter discloses a medicated tampon in the form of a soft porous foam ball made of polyurethane, polyester and polyether materials and impregnated with antibiotic and contraceptive agents for the control of venereal disease and pregnancy.
U.S. Pat. No. 3,545,439 discloses polymeric vaginal rings for releasing medicaments and spermicidal preparations.
Some of the natural and synthetic polymers in acid form have known spermicidal activity. U.S. Pat. No. 2,851,453 discloses an acid carboxymethyl-cellulose preparation used in a tablet. However, a tablet has limited residual effect and is inconvenient to use.
Alginate polymers based on alginic acid salts have previously been used in vaginal preparations and are disclosed in U.S. Pat. No. 3,067,743. The patentee describes the use of an alginate fiber in the formulation of spermicidal preparations. In this case, however, the alginate was used solely as a carrier for spermicidal agents such as quinine or dioctyl sulphosuccinate and any excess alginic acid was converted to soluble sodium or ammonium alginate by neutralization. This preparation does not provide long-acting spermicidal protection nor was any residual alginic acid reported in the compositions.
U.S. Pat. No. 3,653,383 describes a water-absorbent and water-disintegrative open-celled porous sponge made by freeze-drying a gel of sodium and calcium alginate. Such a sponge would not be useful for vaginal contraception since the alginic acid is present only in the nonacidic salt form.
U.S. Pat. No. 4,187,286 discloses a suppository contraceptive containing a spermicidally-active ingredient and in addition alginic acid; the purpose of the alginic acid (present in a proportion of about 13.5-16.5 weight percent) is to form carbon dioxide by neutralization reaction with sodium bicarbonate and as an additional thickening agent in neutral form.